MEMS based sensors have been evolving to combine a sensing element along with the inclusion of several integrated elements inside a “system-in-package” (SIP). Among these integrated elements in the SIP are MEMS devices, interface circuitry, and microprocessor circuitry. These all require specific care when being packaged with the sensing element. Known sensing elements can be based on mechanical, inductive, capacitive, piezoelectric, and piezo-resistive or other sensing techniques.
For sensing attitude, location, or motion, it is known to use accelerometers and gyroscopes. 2-Dimensional accelerometers are widely available as integrated devices and more recently, integrated devices to sense variation also in the third dimension have become available. But such devices have noticeably lower capabilities in calibration along this dimension. In most cases, the device is fabricated on the same substrate which carries the sensing element. Thus the final device is the outcome of two or more single silicon substrates. The interface and the signal processing circuitry are to be integrated as a system.
The sensing element mentioned above typically has a proof mass, which displaces itself elastically with respect to the force, applied on it. This is the basic concept behind accelerometer designs. The proof-mass displaces corresponding to the force which in turn depends on the acceleration. The position of the proof-mass is sensed by one of various known techniques. In the case of capacitive accelerometers, a change in capacitance is related to the displacement of the proof-mass. The capacitor can have one electrode attached to the proof mass and one fixed electrode. These electrodes can be arranged in an interdigitated comb structure. The properties of the proof mass and its elastic support define the range of detection of the sensing element. The concept behind a capacitive accelerometer is to sense the displacement with respect to the change in capacitance.
For sensing the Coriolis effect a solution has been proposed by a device named “Gyroscopes”. This device features the sensing of displacement along the axis of rotation normal to the plane of the structure (proof-mass). Various techniques have been deployed for the sensing action of the displacement. But still the displacement along the three axes and the displacement along the axis of rotation are on different devices. Both the devices can be fabricated using the same technology. For high-end-sensing operation, the known devices are typically fabricated on more than one silicon wafer or by using SOI or relevant technology.
U.S. patent application Ser. No. 2005217372 shows a physical quantity sensor for detecting an angular speed and an acceleration three dimensionally. The sensor includes: a substrate; three angular speed sensors disposed on the substrate; and three acceleration sensors disposed on the substrate. The three angular speed sensors are capable of detecting three components of an angular speed around three axes, each two of which intersect perpendicularly. The three acceleration sensors are capable of detecting three components of an acceleration in another three axes, each two of which intersect perpendicularly. The three axes of the angular speed sensors intersect at one point, and the other three axes of the acceleration sensors intersect at another one point.
The above physical quantity sensor can detect both of the angular speed and the acceleration three dimensionally with high accuracy. Further, in the physical quantity sensor, three detection axes of the angular speed sensors intersect at one point so that the detection accuracy of the angular speed becomes higher. Further, three detection axes of the acceleration sensors intersect at one point so that the detection accuracy of the acceleration becomes higher.
Patent application JP11311521A shows a multiaxial inertia quantity sensor which can be formed integrally by using micromachining technology and can detect angular velocity and linear acceleration in multiple axes. It has comb form intermeshing electrodes at the perimeter of a proof mass to provide rotational vibration to implement the gyroscopic angular sensor. Four electrodes are provided underneath the mass for detecting when the mass is tipped away from its rotation axis. These four electrodes act as capacitive sensors to detect a height of the mass above the substrate. Differences in the heights indicate tipping which indicates rotation according to gyroscopic action. Which two electrodes are higher than the others indicates which axis the rotation is occurring around. Changes in the height of all four sensors, indicates acceleration along the axis of rotation.